These three species are the only true vampire bats; they are the only bats that drink blood. There are also false vampire bats (of the genera Vampyrum and Chrotopterus). These have nasty looking canines, but do not drink blood. (True vampire bats use their incisors to draw blood). Comparatively little is known about the hairy-legged and white-winged species of vampire bat, although the common vampire bat seems to be well studied.

Vampire bats are medium sized bats, ranging from about 7 to 9 centimeters long, with a wingspan of about 20 centimeters. They have stubbier snouts than other bats, and don't have the nose leaf characteristic of other members of the family Phyllostomatidae. Their noses are naked, with U-shaped indentations on the tip. They have small ears and no tails, although they do have webbing between their legs. They are greyish-brown or reddish-brown.

All vampire bats live in the Americas, in tropical and subtropical regions -- from the southern US, through Central America, and throughout large portions of South America. They live in caves, hollow trees, and old mine shafts.

The white-winged and hairy-legged vampire bats feed primarily on birds' and reptiles' blood, while the common vampire bat will more often feed on large mammals (including, at times, humans). Vampire bats have heat sensors to help them locate prey. They will land near their sleeping victim, hop over, and bite them in an area where the blood runs close to the surface (the heat sensors at work again). The bite usually goes unnoticed by the victim. The bats do not suck blood -- they nip a small incision with their incisors, and lick the blood as it leaks out. Their spit contains an anticoagulant (called draculin) to keep the blood flowing smoothly. Their victims do not become members of the living dead.

Vampire bats must feed on blood (they eat nothing else) every couple nights, or they will starve. If they can't find suitable prey, they also have the option of asking another bat to regurgitate some of its dinner into the hungry bat's mouth.

As you might expect, vampire bats can spread disease. They have been known to be carriers of rabies (among animals and humans) and Chagas's disease (among humans). Although the wounds are not serious, the bites can become infected. And finally, it is possible for livestock to lose significant amounts of blood if enough bats bite them often enough. Because vampire bats often feed on chickens and cattle, they are considered pests by many ranchers and farmers, who will poison them.

There are lots more cool vampire bat facts, but most of it is specific to one species of bat. Until these are noded, you'll have to do your own research... And node your research!